1. Field of the Invention
The present invention relates to a plate type fuel cell system in which unit cells generating electricity by an electrochemical reaction between hydrogen and oxygen are arranged on a plane, and more particularly, to a plate type fuel cell system which can prevent a reaction fluid, such as a hydrogen containing fuel, from leaking through a part around an output terminal provided for extracting electricity generated by the electrochemical reaction between hydrogen and oxygen in a stack, thereby enhancing a sealing effect.
2. Description of the Related Art
In general, a fuel cell system generates electricity by an electrochemical reaction between hydrogen obtained from a hydrocarbonaceous fuel, such as natural gas, or a hydrogen containing fuel, such as methanol, etc., and oxygen in air, which has attracted attention as an alternative to solving environmental or resource problems.
The fuel cell system is a power generator that generates the electricity by the electrochemical reaction between hydrogen from the hydrogen containing fuel and air used as an oxidant. Such a fuel cell system basically includes an electric generator for generating the electricity. The electric generator includes a unit cell provided with a membrane electrode assembly that has an electrolyte membrane having selective ion permeability, and anode and cathode electrodes provided on opposite sides of the electrolyte membrane.
Fuel cell systems are classified into Phosphoric Acid Fuel Cells (PAFCs), Molten Carbon Fuel Cells (MCFCs), Solid Oxide Fuel Cells (SOFCs), Polymer Electrolyte Membrane Fuel Cells (PEMFCs), Alkaline Fuel Cells (AFCs), Direct Methanol Fuel Cells (DMFCs), etc. according to the electrolyte used. Among such fuel cell systems, PEMFC systems have relatively excellent output characteristics, operate at low temperature, start quickly and have a short response time, such that PEMFC systems have been widely developed and researched for use as portable power generators. However, PEMFCs systems need a reformer to obtain hydrogen from the hydrogen containing fuel, which puts a limitation on miniaturizing the fuel cell system. To overcome this limitation, a Direct Methanol Fuel Cell (DMFC) has been developed that directly uses methanol as the hydrogen containing fuel.
DMFCs can be classified into stacked DMFCs and plate type DMFCs according to the structures of the unit cells. A stacked DMFC has unit cells which are stacked, and a plate type DMFC has unit cells which are arranged on a plane. However, plate type DMFCs have a problem in that reaction fluid leaks between adjacent unit cells.
FIG. 11 is a view of a fuel cell stack, referred to in Korean Patent Publication No. 2005-60904, in which a sealing member is interposed between a separator and an electrolyte membrane of a membrane-electrode assembly, and having a plurality of grooves formed around the separator contacting the sealing member.
FIG. 12 is a view of a direct liquid fuel cell stack, referred to in Japanese Patent Publication No. 2005-108850, in which a bipolar plate includes a groove having a predetermined depth surrounding an electrode region for anode and cathode electrodes, and a fuel passage hole, which are formed on each surface thereof. A sealing member is formed in the groove.
However, the foregoing fuel cells have a stacked structure, so that there is a limit to apply them to a plate type structure of which the unit cells are arranged on a plane. In other words, it is difficult to effectively prevent the reaction fluid from leaking between the adjacent unit cells of the plate type fuel cell system. In particular, a reaction fluid, such as a hydrogen containing fuel, is likely to leak through a part around an output terminal provided for extracting electricity generated by an electrochemical reaction between hydrogen and oxygen in a stack.